Persons with serious mental illnesses (SMI) face elevated rates of medical comorbidity, and also challenges in effectively managing these health problems. There is an urgent need to develop self-management strategies that allow persons with SMI to more effectively manage their chronic medical illnesses. In general populations, peer-led disease self-management interventions have been demonstrated to be feasible, effective, scalable, and to lead to sustainable improvements in self-management and health outcomes. With funding from an R34 intervention development grant from NIMH, the study team has developed and piloted a modified version of the most widely tested and used peer-led self management program, the Chronic Disease Self- Management Program (CDSMP), for persons with serious mental illness. Two pilot tests of this intervention, the Health and Recovery Peer (HARP) program, demonstrated that the program can be implemented with high engagement, retention, and program fidelity, and can result in effect sizes across a range of outcomes comparable to or greater than those seen in general medical populations. This application proposes to conduct a fully-powered, multisite trial of the HARP program. A total of 400 individuals with serious mental illnesses and one or more chronic medical condition will be recruited from four diverse community mental health clinics in the Atlanta metro region and randomized to the HARP program or usual care. For individuals in the HARP program, two peer educators with SMI and one or more chronic medical condition will lead a six- session, six-week manualized intervention, which helps participants become more effective managers of their chronic illnesses. Follow-up interviews and chart reviews at 3 months, 6 months and one year will assess changes in clinical outcomes, improvement in generic and disease-specific measures of illness self-management, and quality of care. During the final phase of the study, a dissemination strategy building on the CDSMP training infrastructure will allow program participants to lead HARP groups. If successful, this study will establish the first fully peer-led, evidence-based intervention for improving physical self-management in this vulnerable population.